Method and apparatus for maintaining a mixture of products at a certain temperature

ABSTRACT

When maintaining a flow of a mixture of products consisting of a liquid of low to medium viscosity incorporating solid particles at a certain temperature and for a certain period of time the mixture remains for some time in a vessel of a substantially cylindrical shape. The residence time in the vessel of the solid particles mixed with the liquid is controlled separately from the liquid in that the solid particles are carried through the vessel at a regulable speed, independently of the speed of flow of the liquid through the vessel, with the aid of a rotatable conveyor means which is permeable to liquid but not to the solid particles and whose axis of rotation coincides with the axis of the vessel. The solid particles remain mixed with the liquid. The residence time of the solid particles is regulated such that the core of the solid particles attains the same temeprature as the liquid, without the liquid remaining for too long a time at the desired end temperature.

This is a divisional Ser. No. 049,617, filed May 13, 1987, now U.S. Pat.No. 4,802,825.

BACKGROUND OF THE INVENTION

The invention relates to a method and an apparatus for maintaining at acertain temperature, and for a certain period of time, a flow of amixture of products consisting of a liquid of low to medium viscosityincorporating solid particles.

In continuous flow heating or cooling by means of heat exchangers (forexample a tubular heat exchanger) of liquids of low to medium viscosityin which a certain volume percentage of solid particles is contained(for example a soup containing pieces of vegetables and meat), thetransfer of heat is effected from the wall of the heat exchanger via theflowing liquid, the flow of which may or may not be turbulent, to theouter edge of the solid particles, and thence to the core of the latter.With this type of heat transfer the conveying liquid will have reachedthe desired final temperature far more quickly than the core of thesolid particles entrained by the liquid. If for technical reasonsconnected with the process it is necessary for the core of the solidparticles also to attain the same temperature as the liquid, the liquidand the solid particles must be kept at a constant end temperature forso long a time that differences in temperature between the liquid andthe core of the solid particles are eliminated. This may have theconsequence that the liquid remains for too long a time at the desiredend temperature, so that (for example in the case of a food product)undesirable changes of taste and colour occur.

It is possible to subject the liquid and the solid particles separatelyto the desired heat treatment and to mix the two components togetheronly after completion of the process or during the course of the latter.However, this necessitates two heat treatment installations in parallel,while in particular the plant required for the heat treatment of thesolid particles is relatively complicated.

SUMMARY OF THE INVENTION

The present invention now seeks to provide a method and an apparatus inwhich the core of the solid particles attains practically the sametemperature as the liquid, without the liquid remaining for anundesirably long period of time at a certain temperature and without thesolid particles being separated from the liquid for the purpose ofundergoing separate heat treatment.

This aim is achieved through a method of the kind described in thepreamble, in which the mixture remains for some time in a vessel, whichmethod is characterized in that the residence time in the vessel of thesolid particles mixed with the liquid is separately controlled.

It is thus possible to ensure that the residence time in the vessel ofthe liquid and that of the solid particles mixed with the liquid aredifferent and can be controlled in such a manner that the liquid doesnot remain too long at a certain end temperature, while the solidparticles remain sufficiently long in the liquid to ensure that the coreof the fixed particles attain substantially the same temperature as theliquid.

The solid particles are preferably carried through the vessel at aregulable speed with the aid of a conveyor means, independently of thespeed of flow of the liquid through the vessel, while the solidparticles remain mixed with the liquid.

In this way it is very simple to control the residence time in thevessel of the solid particles mixed with the liquid.

The apparatus for applying the method according to the inventioncomprises a vessel in which the mixture of products remains for sometime and to which mixture inlet and outlet pipes are connected, and itis characterized in that a conveyor mechanism acting selectively on thesolid particles is mounted in the vessel, whereby the conveying speedand consequently the residence time of the solid particles in the vesselcan be controlled.

The vessel is preferably substantially cylindrical in shape and theconveyor mechanism preferably comprises a conveyor means which isrotatable at a variable speed and whose axis of rotation coincides withthe axis of the cylindrical vessel, while it is provided with at leastone conveyor element permeable to liquid.

Because of this arrangement, on the one hand the liquid can flow freelythrough the vessel, while on the other hand the solid particlescontained in the liquid can in a simple manner be carried at a certainspeed through the vessel, the conveying speed being adjustable byregulating the speed of rotation of the conveyor means.

In a specific embodiment of the apparatus according to the invention theconveyor element permeable to liquid is situated in a surface extendingfrom the axis of rotation in the outward direction and lying parallel tothe axis of rotation of the conveyor means, and the free peripheral edgeof the conveyor member is situated near the inner side of thecylindrical peripheral wall and the end walls of the vessel. In thisarrangement the conveyor element may be disposed in either a flat planeor a curved surface.

In order to make the conveyor element permeable to liquid, it has asieve-like structure or is provided with slots. In a practicalembodiment of the apparatus according to the invention the conveyorelement consists of a plurality of pins extending perpendicularlyoutwards from the axis of rotation of the conveyor means and spacedapart from each other in the direction of said axis, with their endssituated near the inner side of the cylindrical wall of the vessel.

At the site of the outlet pipe for the mixture an element may beinstalled in the vessel for the purpose of removing the solid particlesfrom the conveyor member, which element consists of a series of pinsdisposed next to one another and spaced apart in the longitudinaldirection of the vessel, which pins extend from the cylindrical wall ofthe vessel towards the axis of rotation of the conveyor means and engagebetween the pins of the conveyor element.

In this way it is ensured that at the site of the outlet pipe theparticles will be removed from the conveyor element and will then bedischarged by means of the liquid flowing through the vessel.

The invention will now be explained by means of a description of anexample of embodiment of the invention and with reference to thedrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows schematically an embodiment of an apparatus according tothe invention in a section perpendicular to the axis of rotation of theconveyor member,

FIG. 2 is a section of the apparatus shown in FIG. 1, taken on the lineII--II,

FIG. 3 shows schematically another embodiment of an apparatus accordingto the invention in a similar section to FIG. 1,

FIG. 4 is a section of the apparatus shown in FIG. 3, taken on the lineIV--IV, and

FIG. 5 shows schematically in perspective a conveyor element mounted ona shaft and consisting of pins, with an element engaging between themfor removing the solid particles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus according to the invention is intended to form part of aheat treatment installation in which a liquid and solid particlescontained therein undergo a certain heat treatment. The apparatusaccording to the invention is therefore also referred to as a unit forkeeping hot.

The embodiment of the apparatus shown in FIGS. 1 and 2 is given thegeneral designation 10 and comprises a substantially closed cylindricalvessel 11 having a peripheral wall 12 and two end walls 13 and 14. Aninlet pipe 15 and an outlet pipe 16 are connected to the peripheralwall.

A rotating bladed wheel 17 is mounted inside the vessel 11 and consistsof a shaft 18 on which blades 19, of which in the present case there aresix, are mounted. The axis of rotation of the bladed wheel coincideswith the axis of the cylindrical vessel 11. The free peripheral wall ofeach of the blades 19 is situated near the inner side of the cylindricalperipheral wall 12 and the two end walls 13 and 14 of the vessel 11. Theblades 19 are permeable to liquid, and for this purpose, as shown inFIG. 2, have a sieve-like structure. It is however also possible for theblades 19 to be provided with slots.

The bladed wheel 17 can be driven at an adjustable speed of rotation bymeans of a shaft passing through one or both end walls 13, 14. The drivemeans is not shown in the drawings.

The mixture which has to be kept at a certain temperature for a certainperiod of time, and which consists of a liquid of low to mediumviscosity and of solid particles contained therein, can be fed via theinlet pipe 15 and discharged through the outlet pipe 16. The liquid canflow directly from the inlet pipe 15 via the opening in the blades,freely in all directions, through the vessel towards the outlet pipe 16.The liquid will for this purpose take the path of least resistance.

The solid particles 20 contained in the liquid will on the other hand beheld back by the rotating blades 19 and thus prevented from taking theshortest route from the inlet pipe 15 to the outlet pipe 16. The solidparticles are caught between the blades 19 of the driven bladed wheeland carried in the direction of rotation of the latter until they reachthe outlet pipe 16. The solid particles 20 there leave the spacesbetween the blades 19, being entrained by the liquid flowing through thevessel 11, and reach the outlet pipe 16. Adjustment of the speed ofrotation of the bladed wheel 17 enables the residence time of the solidparticles 20 in the vessel 11 to be determined irrespective of theresidence time of the liquid in the vessel. The residence time of thesolid particles 20 in the vessel can be adjusted in such a manner thatthere is sufficient time for the core of the solid particles 20 to reachthe same temperature as that of the liquid. In this way it is ensuredthat both the liquid and the solid particles in the mixture will havesubstantially the same temperature when they leave the apparatus via theoutlet pipe 16.

FIG. 3 and 4 show another embodiment of the apparatus according to theinvention, which is given the general designation 21. The apparatusagain comprises a substantially cylindrical vessel 22 having acylindrical peripheral wall 23 and end walls 24 and 25. An inlet pipe 26and an outlet pipe 27 are likewise connected to the vessel, the inletpipe 26 and the outlet pipe 27 being situated rather differently fromthe arrangement shown in FIGS. 1 and 2. In this embodiment also use ismade of a bladed wheel 28, which consists of blades 30, of which in thiscase there are four, mounted on a shaft 29.

Each blade 30 consists of a plurality of pins 31 extending outwardsperpendicularly from the shaft 29 and spaced apart in the direction ofthe latter, their ends being situated near the inner side of thecylindrical wall 23 of the vessel 22. In the embodiment illustrated thepins 31 are curved. It is however also possible for the pins to bestraight.

The operation of the apparatus shown in FIGS. 3 and 4 is identical tothat of the apparatus shown in FIGS. 1 and 2.

For the purpose of removing the solid particles 20 from the blades 30,there is provided in the vessel 22, at the site of the outlet pipe 27,an element 32 consisting of a series of pins 33, which are disposed nextto one another and spaced apart in the longitudinal direction, and whichextend from the cylindrical wall 23 of the vessel 22 towards the shaft29 and engage between the pins 31 of the blades 30. It can thus beensured that no solid particles will remain behind on the blades andthus be able to make a second passage around the vessel, in which casethe residence time of these solid particles would exceed the maximumresidence time. FIG. 5 shows schematically the shaft 29 with a blade 30,consisting of pins 31, mounted on it, together with the means 32consisting of pins 33. Solid particles 20 which may have been jammedbetween the pins 31 are so-to-speak pushed by the pins 33 in thelengthwise direction of the pins 31, out of the slots formed between thelatter.

With the apparatus according to the invention it is thus possible tocontrol the residence time of the solid particles in a mixtureconsisting of a liquid of low to medium viscosity and solid particlescontained therein, independently of the residence time of the liquid inthe vessel, without the solid particles being separated from the liquid.It can thus be ensured that the solid particles will attain the desiredend temperature even in their cores, without the liquid remaining toolong at the end temperature, which in the case of foodstuffs, forexample, could lead to undesirable changes of taste and colour.

What is claimed is:
 1. An apparatus for maintaining at a certaintemperature, and for a certain period of time, a flow of a mixture ofproducts which includes a liquid of low to medium viscosity having solidparticles contained therein, comprising:(a) a vessel for holding amixture of products therein, the vessel having a peripheral inner wall;(b) a mixture inlet pipe connected to the vessel and in fluidcommunication therewith; (c) a mixture outlet pipe connected to thevessel and in fluid communication therewith; and (d) means forcontrolling residence time in the vessel of substantially all solidparticles which pass thereinto from the inlet pipe, the residence timecontrolling means comprising a conveyor mechanism having a central shaftdisposed axially in the vessel, and at least one conveyor element whichextends from the central shaft substantially radially outwardly in thevessel, the conveyor element extending close to the peripheral innerwall of the vessel to prevent passage of solid particles between theconveyor element and the inner wall.
 2. The apparatus of claim 1,wherein the vessel is substantially cylindrical in shape and both theinlet pipe and outlet pipe are connected thereto at a radially outermostsurface thereof, and the conveyor mechanism is rotatable at a variablespeed, and wherein the conveyor element is permeable to liquid.
 3. Theapparatus of claim 2, wherein the conveyor element permeable to liquidis situated in a surface extending from the axis of rotation in anoutward direction, and wherein the conveyor element has a freeperipheral edge situated near the inner side of the cylindricalperipheral wall and the end walls of the vessel, whereby the conveyorelement limits the maximum speed of the solid particles to the speed ofthe conveyor element.
 4. An apparatus as claimed in claim 3, wherein thesurface in which the conveyor element is situated is a flat plane.
 5. Anapparatus as claimed in claim 3, wherein the surface in which theconveyor element is situated is a curved surface.
 6. The apparatus ofclaim 3, wherein the conveyor element comprises a plurality of pinsextending transversely outwardly from the axis of rotation of theconveyor means and spaced apart from each other in the direction of saidaxis, the outermost ends of the pins being situated near the inner sideof the cylindrical wall of the vessel.
 7. The apparatus of claim 6,further comprising a series of pins disposed next to one another andspaced apart in the longitudinal direction of the vessel, which pinsextend from the cylindrical wall of the vessel towards the axis ofrotation of the conveyor means and engage between the pins of theconveyor element.
 8. An apparatus as claimed in claim 2, wherein theconveyor element has a sieve-like structure.
 9. An apparatus as claimedin claim 2, wherein the conveyor element is provided with slots.
 10. Theapparatus of claim 1, wherein the mixture outlet pipe is the sole andexclusive avenue for liquid to depart from the vessel.
 11. The apparatusof claim 10, wherein the vessel is substantially cylindrical in shapeand both the inlet pipe and outlet pipe are connected thereto at aradially outermost surface thereof.